Deflection yoke core slotted for vertical toroidal coils



M. J. OBERT I 3,321,724

' May '23, 1967 DEFLECTION YQKE CORE SLOTTED FOR VERTICAL TOROIDAL COILS I I Filed Feb. 4,1965

2' Sheets-Sheet 1 I INVENTOR. v/l//1 \r //|///u/uvJ 055w 141! file May 23, 1967 I J. OBERT 7 3,321,724 DEFLECTION YOKE CORE SLOTTED FOR VERTICAL TOROIDAL COILS Filed Feb. 4, I 1965 INVENTOR.

2 Sheets-Sheet 2 United States Patent 3,321,724 DEFLECTION YOKE CORE SLOTTED FOR VERTICAL TOROIDAL COILS Maximilian J. Obert, Indianapolis, Ind., assignor to Radio Corporation of America, a corporation of Delaware Filed Feb. 4, 1965, Ser. No. 430,416 4 Claims. (Cl. 335-213) This invention relates to electromagnetic deflection yokes for cathode ray tube beams and particularly to the ferromagnetic cores used with such yokes.

Electromagnetic beam deflection yokes usually 'are provided with ferromagnetic cores for the purpose of increasing the efliciency of these yokes in deflecting the electron beams of cathode ray tubes. The cores encircle the active conductors of the coils of the deflection yokes and provide low reluctance return paths for the flux genera-ted by the coils. In a currently popular type of deflection yoke the horizontal coils are of saddle form and the vertical coils are of toroidal form. Accurate positioning of each coil comprising a pair of horizontal or vertical coils relative to one another is required to minimize distortion of the raster scanned by the electron beam. Additionally each of the pair of horizontal coils must have its centerline at right angles to the centerline of each of the pair of vertical coils. must be accurately located 180 from one another in order to avoid the possibility of a trapezoidal or other undesired deformation of the scanned raster.

It, therefore, is one object of the present invention to provide a ferromagnetic core for a deflection yoke which has facilities for accurately positioning the toroidal vertical coils relative to one another so as to minimize raster distortion.

Another requirement of deflection yokes, particularly those for deflecting electron beams through relatively large angles, is the avoidance of beam defocusing. Fringe fields at the rear end of such deflection yokes adjacent to the electron gun and focus electrode of the tube have been found to be one of the factors tending to cause beam defocusing.

Another object of the invention is to provide a ferromagnetic core for a deflection yoke which is designed to reduce the fringe field at the rear of the yoke so as to minimize beam defocusing. I

It is desirable, in the manufacture of deflection yokes with toroidal coils, to wind these coils at relatively high speed with wire which is kept under substantial tension so that the definite winding pattern required by the design, and determined by the core shape, is accurately maintained. These requirements have been met in the past by winding over the properly shaped ferrite core, with a sheet of insulating material between the wire and the core so as to avoid rupturing the wire insulation in places where it may come into contact with edges of the core.

Still another object of the invention is to provide a ferromagnetic core for a deflection yoke which is so constructed as to require no insulation between it and the toroidal coils wound upon it.

According to the present invention the ferromagnetic core of a deflection yoke has a pair of diametrically opposed slots formed internally thereof and extending from the rear end to the front end thereof. The toroidal coils may be wound in the slots and thereby will be accurately positioned 180 from one another. The core also may have a pair of recesses formed in the rear end thereof in communication with the respective slots. When the toroidal coils are received in these recesses the undesired fringe field at the rear of the yoke is reduced. Additionally, the front and rear ends of the core may be rounded, at least in the regions of the slots and recesses, so as to In particular, the toroidal vertical coilssubstantially avoid rupture of the insulation of the wire of the toroidal coils.

For a better understanding of the invention reference now will be made to the following description which is taken in conjunction with the accompanying drawings, of which:

FIGURE 1 is a perspective view of the yoke embodying a core in accordance with the invention;

FIGURE 2 is a somewhat enlarged sectional view taken on the line 22 of FIGURE 1 showing the relationship of the saddle type horizontal coils, the toroidal type vertical coils and the insulation between these different coils;

FIGURE 3 is a view taken on the line 3-3 of FIG- URE 2 and is a transverse section toward the rear, or electron gun, end of the yoke showing the interlocking relationship between the horizontal and vertical;

FIGURE 4 is a top view of the core showing the recesses formed in the rear end thereof;

FIGURE 5 is a front view of the core embodying the present invention showing its oval transverse configuration; and

FIGURE 6 is a side view of the core.

The general arrangement of a deflection yoke embodying the invention is shown in FIGURES l, 2 and 3 in which corresponding parts are identified by the same reference characters. The yoke comprises a pair of saddle type horizontal coils 11 and 12 which have active conductors 13 and 14, respectively, and which extend generally longitudinally of the cathode ray tube (not shown) with which the yoke may be used. The active conductors 13 on opposite sides of the yoke of the coil 11 are joined at the forward or screen end of the yoke by end turns 15 and at the rear or electron gun end by end turns 16. Similarly the coil 12' is provided with forward end turns 17 and rear end turns 18.

A toroidal type vertical deflection coil 19 is disposed entirely within the window formed between the active conductors such as 13 of coil 11. Similarly, a toroidal vertical coil 21 is mounted in the window space between the active conductors 14 of the horizontal coil 12. An in sulator 22 is placed on the undersides of the horizontal coils 11 and 12 so as to insulate these coils from a ferromagnetic core 23 which encircles the coils. The insulator 22, also, provides a small insulating barrier between the outer extremities of vertical coils 19 and 21 and the window edges of horizontal coils 11 and 12, respectively. The insulator, which comprises two identical halves for ease of assembly, additionally protectively envelopes the end turns 16 and 18 of the horizontal coils 11 and 12 as shown in FIGURE 2. The core 23, in a direction longitudinally of the yoke, has a rear straight portion 24 and a forward flared portion 25. This configuration corresponds generally to the overall shape of the deflection yoke so that the relatively straight portion encircles the tubular neck section of the cathode ray tube and the flared portion encircles the bulb section of the tube. The insulator 22 also has inwardly extending ribs 26 and 27 to separate the active conductors such as 13 and 14, respectively, of the hor'montal coils 11 and 12 and to accurately position the coils in the yoke.

As may be seen more clearly in FIGURE 2, each of the toroidal coils such as 21 is made up of a number of turns of wire around the core 23. This figure also shows the physical relationship between the vertical deflection ooil such as 21 and the horizontal coil such as 12. 7

FIGURE 3 shows the oval configuration of the core 23 in which are indicated the major axis 28 and minor axis 29. The active conductors of the horizontal coils 11 and 12 are disposed generally at the extremities of the major axis 28 of the core and the vertical coils 19 and 21 are located generally at axis 29 of the core. It will be understood that, with the the extremities of the minor.

3 illustrated conductor distribution of the horizontal coils 11 and 12 and the location of these coils at the extremities of the major axis 28 together with the disposition of the vertical coils 19 and 21 within the windows formed between the active conductors of the horizontal coils, the internal shape of the yoke is substantially circular so that it may fit snugly over the circular parts of the cathode ray tube with which it is to be used.

Details of the ferromagnetic core in accordance with the invention are more clearly shown in FIGURES 4, and 6. The core 23 is oval shaped as previously described having a major axis 28 and a minor axis 29. Slots 31 and 32 are provided internally of the core 23 at opposite ends of the minor axis 29. These slots extend generally from the large forward end 33 of the core 23 to the relatively small rear end 34 of the core. These slots have their maximum depths at the rear of the core as indicated at points 35 and decrease in depth toward the front of the core, finally merging with the front end 33 as indicated at points 36. As indicated more clearly in FIGURES 4 and 6 the slots 31 and 32 terminate respectively in recesses 37 and 38 formed in the rear ends 34.

The purpose of the slots 31 and 32 and recesses 37 and 38 is to receive the toroidally wound vertical coils of the deflection yoke. By means of such features the toroidal coils may be placed on the core without any uneven building up of the coil at the front and rear ends of the yoke. These features also enable the accurate positioning of the vertical coils relative to one another and to the horizontal coils and thereby minimize distortions such as trapezoidal misshaping of the raster scanned by the electron beam. By slotting and recessing the core 23 to receive the vertical coils 19 and 21 as described the inside dimensions of the core may be made smaller, thereby bringing the core closer to the electron beam of the cathode ray tube which significantly increases the deflection efliciency of the yoke. Also, the recesses 37 and 38 at the rear end 34 of the core 23 enable the positioning of the conductors of the toroidal coils in such a way as to reduce the extent of the fringe field produced thereby at the back of the yoke and consequently minimize the amount of beam defocusing which otherwise might result from a fringe field reaching into the electron gun region of the cathode ray tube.

The front and rear ends 33 and 34, respectively, of the core 23 are rounded as indicated at points 39 and 40 so that the toroidal vertical coils may be wound on the core at high speed under considerable tension without any insulation being provided between the wire and the core except for the enamel or other type of insulation provided on the wire itself. In order to insure such rounding of the core 23 it may be necessary to strike off (such as by grinding) any sharp edges 41 left by the molding process, at least in those regions of the core over which the vertical coils 19 and 21 are to be wound.

As is the practice in placing toroidal windings on ferromagnetic cores, the core 23 is molded of suitable ferrite material in its final form such as shown in FIGURES 4, 5 and 6. It is then broken into two pieces approximately along lines 42 and 43 corresponding generally with the major axis 28, after which each part is placed in a winding machine for the placement thereon of the two toroidal coils. It has been found that, with a core such as that described and embodying the present invention having features such as the rounded front and rear ends indicated at points 38 and 39, the fabrication of such yokes may be materially facilitated without the provision of extra insulation which previously has been found necessary between the toroidal windings and the cores upon which they are wound. It is, however, advisable that the ferrite core be fabricated from a mixture, which after processing, has sufficient skin or surface resistance to provide the necessary electrical isolation of the vertical toroidal coils from the yoke without any additional insulation.

What is claimed is:

1. In an electromagnetic yoke for deflecting the electron beam of a cathode ray tube in two orthogonal directions:

a ferromagnetic core encircling said cathode ray tube and having an oval transverse cross-section with a minor axis in one of said orthogonal directions and a major axis in the other of said orthogonal directions.

said core having a pair of slots formed internally thereof centered about the extremities of said minor axis and extending from the rear end to the front end of said core,

said core also having a pair of recesses formed in said rear end in communication with said respective slots,

and said front and rear ends of said core being rounded at least in the regions of said slots and recesses so that toroidal type coils may be supported by and in direct physical contact with said slots and recesses without rupture of the insulation of the wire of said coils.

2. In an electromagntic yoke including a pair of toroidal type coils for deflecting the electron beam of a cathode ray tube in one of two orthogonal directions, both of said coils having active conductors extending longitudinally of said cathode ray tube;

a ferromagnetic core encircling said cathode ray tube and having an oval transverse cross-section with a minor axis in said one orthogonal direction and a major axis in the other of said orthogonal directions,

said core being adapted to encompass the active conductors of said coils adjacent the extremities of said minor axis,

said core having a pair of slots formed internally thereof centered about the extremities of said minor axis and extending from the rear end to the front end of said core,

said core also having a pair of recesses formed in said rear end in communication with said respective slots,

and said front and rear ends of said core being rounded at least in the regions of said slots and recesses so that said toroidal type coils may be supported by and in direct physical contact with said slots and recesses without rupture of the insulation of the wire of said coils.

3. In the combination of a cathode ray tube having a tubular neck section joined to a generally conical bulb section and an electromagnetic yoke including a pair of toroidal type coils for deflecting the electron beam of said cathode ray tube in one of two orthogonal directions:

a ferromagnetic core for said yoke encircling said cathode ray tube in the region of the junction of said neck and bulb sections,

said core longitudinally having a relatively small portion beginning at the rear end of said core and encircling said neck section and a relatively large portion ending at the front end of said core and encircling said bulb section,

substantially all transverse cross-sections of said core being of oval configuration with a minor axis in said one orthogonal direction and a major axis in the other of said orthogonal directions,

said core having a pair of slots formed internally thereof centered about the extremities of said minor axis and extending from said rear end to said front end, the depth of said slots diminishing from a maximum at said rear end to a merger with said front end,

said core also having a pair of recesses formed in said rear end in communication with said respective slots,

and said front and rear ends of said core being rounded at least in' the regions of said slots and recesses so that said toroidal type coils may be supported by 5 and in direct physical contact with said slots and recesses without rupture of the insulation of the wire of said coils.

4. In the combination of a cathode ray tube having a tubular neck section joined to a generally conical bulb section and an electromagnetic yoke including a pair of toroidal type coils fordeflecting the electron beam of said cathode ray tube in one of two orthogonal directions:

a ferromagnetic core for said yoke encircling said cathode ray tube in the region of the junction of said neck and bulb sections,

said core longitudinally having a relatively straight portion beginning at the rear end of said core and encircling said neck section and a flared portion ending at the front end of said core and encircling said bulb section,

substantially all transverse cross-sections of said core being of oval configuration with a minor axis in said one orthogonal direction and a major axis in the other of said orthogonal directions,

said core having a pair of slots formed internally thereof centered about the extremities of said minor axis and extending from said rear end to said front end, the depth of said slots diminishing from a maximum at said rear end to a merger with said front end,

said core also having a pair of recesses formed in said rear end in communication with said respective slots,

and said front and rear ends of said core being rounded at least in the regions of said slots and recesses so that said toroidal type coils may be supported by and in direct physical contact with said slots and recesses without rupture of the insulation of the wire of said coils.

References Cited by the Examiner UNITED STATES PATENTS 2,692,355 10/1954 Sickles et al. 335-213 3,035,198 5/1962 Skoyles 31376 3,246,192 4/1966 Torsch 31376 20 JAMES W. LAWRENCE, Primary Examiner.

R. SEGAL, Assistant Examiner. 

1. IN AN ELECTROMAGNETIC YOKE FOR DEFLECTING THE ELECTRON BEAM OF A CATHODE RAY TUBE IN TWO ORTHOGONAL DIRECTIONS: A FERROMAGNETIC CORE ENCIRCLING SAID CATHODE RAY TUBE AND HAVING AN OVAL TRANSVERSE CROSS-SECTION WITH A MINOR AXIS IN ONE OF SAID ORTHOGONAL DIRECTIONS AND A MAJOR AXIS IN THE OTHER OF SAID ORTHOGONAL DIRECTIONS. SAID CORE HAVING A PAIR OF SLOTS FORMED INTERNALLY THEREOF CENTERED ABOUT THE EXTREMITIES OF SAID MINOR AXIS AND EXTENDING FROM THE REAR END TO THE FRONT END OF SAID CORE, SAID CORE ALSO HAVING A PAIR OF RECESSES FORMED IN SAID REAR END IN COMMUNICATION WITH SAID RESPECTIVE SLOTS, AND SAID FRONT AND REAR ENDS OF SAID CORE BEING ROUNDED AT LEAST IN THE REGIONS OF SAID SLOTS AND RECESSES SO THAT TOROIDAL TYPE COILS MAY BE SUPPORTED BY AND IN DIRECT PHYSICAL CONTACT WITH SAID SLOTS AND RECESSES WITHOUT RUPTURE OF THE INSULATION OF THE WIRE OF SAID COILS. 